Measurement method and encoder device, and exposure method and device

ABSTRACT

There is provided an encoder device to measure a relative moving amount between first and second members. The encoder device includes: a reflective-type diffraction grating on the first member; a light source unit to radiate a measuring light; a first optical member on the second member; a first and second reflecting units on the second member that cause first and third diffracted lights generated via diffraction of the measuring light and having orders different from each other to come into the diffraction grating respectively, and cause second and fourth diffracted lights generated via diffraction of the first and third diffracted lights respectively to come into the first optical member; photo-detectors configured to detect interference lights between two diffracted lights and other light beam respectively; and a measuring unit to obtain the relative moving amount by using detection signals from the photo-detectors.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.15/964,230 filed Apr. 27, 2018 which is a continuation of U.S.application Ser. No. 14/397,312 filed Feb. 10, 2015, which is a U.S.national phase entry of International Application No. PCT/JP2013/057309which was filed on Mar. 14, 2013 claiming the conventional priority ofProvisional Patent Application No. 61/638,719, filed on Apr. 26, 2012and the disclosures of the above applications are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present teaching relates to a measurement method and an encoderdevice which measure a relative moving amount between members movingrelative to each other; an exposure technology using the measurementmethod and the encoder device; and a method for producing a device usingthe exposure technology.

BACKGROUND ART

In an exposure apparatus such as a so-called stepper or scanningstepper, which is used in the photolithography process for producingelectronic devices (micro devices) such as semiconductor devices, etc.,a laser interferometer is conventionally used to measure the position ofa stage moving a substrate as the exposure objective. In the laserinterferometer, however, the optical path for a measuring beam is longand tends to vary (change), and thus there is a short-term change(variation) of the measured value caused due to the temperaturefluctuation (change, variation) in the atmosphere on the optical path,which is becoming all the more unignorable.

In order to address the above-described situation, for example, there isutilized in recent years a so-called encoder device (interfering typeencoder) which irradiates a measuring light (measuring light beam)composed of a laser light (laser light beam) onto a diffraction gratingfixed on a member (stage, etc.), and which measures a relative movingamount of the stage having the diffraction grating provided thereon,from a detection signal obtained by photo-electrically converting aninterference light (interference light beam) generated by interferencebetween a diffracted light (diffracted light beam) generated from thediffraction grating and other diffracted light or a reference light(reference light beam) (see, for example, U.S. Pat. No. 8,134,688). Thisencoder device has more excellent short-term stability in the measuredvalue than the laser interferometer, and has become to be capable ofachieving a resolving power which is close to that of the laserinterferometer.

SUMMARY

In a conventional encoder device, a diffracted light generated from thediffraction grating is reflected by a planar mirror, etc. Accordingly,there is a fear that when the height of a grating pattern surface of thediffraction grating is changed or varied, the diffracted light from thegrating pattern surface might be shifted relative to the otherdiffracted light or the reference light, thereby lowering the signalintensity of the interference light.

An aspect of the present teaching is to address such a problem describedabove, and an object of the aspect is to prevent the lowering of signalintensity of the interference light caused, when the relative movingamount is measured by using the diffraction grating, due to a change inthe height of the grating pattern surface.

According to a first aspect of the present teaching, there is providedan encoder device configured to measure a relative moving amount betweena first member and a second member, which is supported to be movablerelative to the first member at least in a first direction. The encoderdevice includes: a reflective-type diffraction grating provided on thefirst member and having a grating pattern of which periodic direction isat least the first direction; a light source unit configured to radiatea measuring light; a first optical member provided on the second memberand causing the measuring light to come substantially perpendicularlyinto a surface of the grating pattern of the diffraction grating; afirst reflecting unit provided on the second member, causing a firstdiffracted light, which is generated, via diffraction of the measuringlight, from the diffraction grating in the first direction, to come intothe diffraction grating, and causing a second diffracted light, which isgenerated, via diffraction of the first diffracted light, from thediffraction grating, to come into the first optical member; a secondreflecting unit provided on the second member, causing a thirddiffracted light, of which order is different from that of the firstdiffracted light and which is generated, via diffraction of themeasuring light, from the diffraction grating in the first direction, tocome into the diffraction grating, and causing a fourth diffractedlight, which is generated, via diffraction of the third diffractedlight, from the diffraction grating, to come into the first opticalmember; a first photo-detector configured to detect an interferencelight generated by interference between the second diffracted light viathe first optical member and other light beam than the second diffractedlight; a second photo-detector configured to detect an interferencelight generated by interference between the fourth diffracted light viathe first optical member and other light beam than the fourth diffractedlight; and a measuring unit configured to obtain the relative movingamount between the first member and the second member by using detectionsignals from the first and second photo-detectors.

According to a second aspect of the present teaching, there is providedan encoder device configured to measure a relative moving amount betweena first member and a second member, which is supported to be movablerelative to the first member at least in a first direction. The encoderdevice includes a reflective-type diffraction grating provided on thefirst member and having a grating pattern of which periodic direction isat least the first direction; a light source unit configured to radiatea measuring light; a first optical member provided on the second memberand causing the measuring light to come into a first position on asurface of the grating pattern of the diffraction grating; a firstreflecting unit provided on the second member and causing a firstdiffracted light, which is generated, via diffraction of the measuringlight, from the diffraction grating in the first direction, to come intoa second position on the diffraction grating; and a second reflectingunit provided on the second member and causing a third diffracted light,of which order is different from that of the first diffracted light andwhich is generated, via diffraction of the measuring light, from thediffraction grating in the first direction, to come into a thirdposition on the diffraction grating. Both of the second position and thethird position are different, in a second direction perpendicular to thefirst direction, from a first line segment at which a first plane andthe reflective-type diffraction grating cross or intersect, the firstplane including the first position, a path of the first diffracted lighttravelling from the diffraction grating to the first reflecting unit anda path of the second diffracted light travelling from the diffractiongrating to the second reflecting unit.

Further, according to a third aspect of the present teaching, there isprovided an exposure apparatus configured to expose an object to beexposed with a pattern, the exposure apparatus including: a frame; astage configured to support the object and configured to be movablerelative to the frame at least in a first direction; and the encoderdevice as defined in the first aspect or the second aspect configured tomeasure a relative moving amount between the frame and the stage atleast in the first direction.

Further, according to a fourth aspect of the present teaching, there isprovided a measuring method for measuring a relative moving amountbetween a first member and a second member, which is supported to bemovable relative to the first member at least in a first direction. Thismeasuring method includes: causing a measuring light to comesubstantially perpendicularly into a surface of a grating pattern, ofwhich periodic direction is at least the first direction, of areflective-type diffraction grating provided on the first member, via afirst optical member provided on the second member; causing a firstdiffracted light, which is generated, via diffraction of the measuringlight, from the diffraction grating in the first direction, to come intothe diffraction grating by a first reflecting unit provided on thesecond member, and causing a second diffracted light, which isgenerated, via diffraction of the first diffracted light, from thediffraction grating, to come into the first optical member by the firstreflecting unit; causing a third diffracted light, of which order isdifferent from that of the first diffracted light and which isgenerated, via diffraction of the measuring light, from the diffractiongrating in the first direction, to come into the diffraction grating bya second reflecting unit provided on the second member, and causing afourth diffracted light, which is generated, via diffraction of thethird diffracted light, from the diffraction grating, to come into thefirst optical member by the second reflecting unit; detecting aninterference light generated by interference between the seconddiffracted light via the first optical member and other light beam thanthe second diffracted light; detecting an interference light generatedby interference between the fourth diffracted light via the firstoptical member and other light beam than the fourth diffracted light;and obtaining the relative moving amount between the first member andthe second member based on the detection results.

Further, according to a fifth aspect of the present teaching, there isprovided a measuring method for measuring a relative moving amountbetween a first member and a second member, which is supported to bemovable relative to the first member at least in a first direction. Thismeasuring method includes: causing a measuring light to come into afirst position on a grating pattern, of which periodic direction is atleast the first direction, of a reflective-type diffraction gratingprovided on the first member; causing a first diffracted light, which isgenerated, via diffraction of the measuring light, from the diffractiongrating in the first direction, to come into a second position on thediffraction grating; and causing a third diffracted light, of whichorder is different from that of the first diffracted light and which isgenerated, via diffraction of the measuring light, from the diffractiongrating in the first direction, to come into a third position on thediffraction grating. Both of the second position and the third positionare different, in a second direction perpendicular to the firstdirection, from a first line segment at which a first plane and thereflective-type diffraction grating cross or intersect, the first planeincluding the first position, a path of the first diffracted lighttravelling from the diffraction grating to the first reflecting unit anda path of the second diffracted light travelling from the diffractiongrating to the second reflecting unit.

Further, according to a sixth aspect of the present teaching, there isprovided an exposure method for exposing an object to be exposed with apattern, the object being supported by a stage configured to be movablerelative to a frame at least in a first direction, the exposure methodincluding, measuring a relative moving amount between the stage and theframe at least in the first direction by using the measuring method asdefined in the fourth aspect or the fifth aspect.

Further, according to a seventh aspect of the present teaching, there isprovided a method for producing a device, including a lithography step,wherein an object is exposed in the lithography step by using theexposure apparatus as defined in the third aspect or the exposure methodas defined in the sixth aspect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of an encoder according to a first embodiment ofthe present teaching.

FIG. 2A is a perspective view illustrating main components or parts ofan X-axis interferometer unit in FIG. 1; FIG. 2B is a plan viewillustrating irradiation positions of a measuring light and a diffractedlight in FIG. 2A; and FIG. 2C is an illustrative view illustrating openangles of the measuring light and a reference light.

FIG. 3A is a diagram depicting optical paths of ±1 order diffractedlights in an X direction in the X-axis interferometer unit of FIG. 2A,and FIG. 3B is a diagram depicting optical paths of ±1st orderdiffracted lights in an Y-axis interferometer unit.

FIG. 4A is a diagram depicting a change in the optical path of thediffracted light when the relative height of a grating pattern surfaceis changed in the X-axis interferometer unit of FIG. 2A, and FIG. 4B isa diagram depicting a change in the optical path of the diffracted lightwhen the grating pattern surface is relatively inclined.

FIG. 5A is a diagram illustrating main components or parts of an X-axisinterferometer unit according to a first modification of the presentteaching, and FIG. 5B is a perspective view depicting a roof mirror inFIG. 5A.

FIG. 6 is a diagram illustrating main components or parts of an X-axisinterferometer unit according to a second modification of the presentteaching.

FIG. 7 is a plan view depicting a part of a detection head according tothe first modification.

FIG. 8 is a plan view depicting main components or parts of a detectionhead according to the second modification.

FIG. 9 is a schematic view depicting the construction of an exposureapparatus according to a second embodiment of the present teaching.

FIG. 10 is a plan view depicting an example of the arrangement of adiffraction grating provided on a wafer stage depicted in FIG. 9 and aplurality of detection heads.

FIG. 11 is a block diagram depicting a control system of the exposureapparatus depicted in FIG. 9.

FIG. 12 is a flowchart indicating an exemplary measurement method.

FIG. 13 is a flowchart indicating an example of a method for producingan electronic device.

DESCRIPTION OF EMBODIMENTS First Embodiment

A first embodiment of the present teaching will be explained withreference to FIG. 1 to FIG. 4B. FIG. 1 is a plan view depicting anencoder 10 according to the embodiment. In FIG. 1, as an example, asecond member 7 is disposed to be movable three-dimensionally relativeto a first member 6. The following explanation will be made assumingthat the X axis and the Y axis extend parallel to two relative-movementdirections, respectively, which are orthogonal to each other and inwhich the second member 7 is movable relative to the first member 6, andthe Z axis extends in a relative movement direction which is orthogonalto a plane (XY plane) defined by the X axis and the Y axis and in whichthe second member is movable relative to the first member 6. Further,angles of rotation (inclinations) about the axes parallel to the X axis,the Y axis, and the Z axis are designated as angles in θx, θy, and θzdirections respectively.

In FIG. 1, the encoder 10 has a two-dimensional diffraction grating 12which has a flat plate-shape (planar shape) substantially parallel tothe XY plane, and which is fixed to the upper surface of the firstmember 6; a detection head 14 which is fixed to the second member 7; alaser light source 16 and an optical fiber 17 which supply a laser light(laser light beam) for measurement to the detection head 14; opticalfibers 39XA, 39XB, 39YA, 39YB, and 39C which transmit or deliver aplurality of interference lights generated in the detection head 14;photoelectric sensors 40XA, 40XB, 40YA, 40YB, and 40C, such asphotodiodes, which receive the interference lights supplied via theoptical fibers 39XA, 39XB, 39YA, 39YB, and 39C to output detectionsignals; and a measurement calculation unit 42 (42X, 42Y, 42T) whichprocesses the detection signals to obtain movement amounts of athree-dimensional relative movement of the second member 7 relative tothe first member 6, that is movement amounts in the X, Y, and Zdirections. The detection head 14 includes an X-axis interferometer unit15X which irradiates a measuring light to the diffraction grating 12 togenerate a plurality of interference lights formed or generated byinterference between a reference light and a plurality of diffractedlights generated in the X direction from the diffraction grating 12; anY-axis interferometer unit 15Y which irradiates the measuring light tothe diffraction grating 12 to generate a plurality of interferencelights formed or generated by interference between a reference light anda plurality of diffracted lights generated in the Y direction from thediffraction grating 12; other optical members; and support members 35Xand 35Y which are fixed to the second member 7 to support the opticalmembers and in which a plurality of openings, which allow light beam topass through the inside thereof, are formed.

The diffraction grating 12 has a grating pattern surface 12 b which issubstantially parallel to the XY plane; a two-dimensional gratingpattern 12 a, which has a predetermined period (pitch) p in each of theX and Y directions and which is a phase-type and reflective-typegrating, is formed on the grating pattern surface 12 b. The periods p inthe X and Y directions of the grating pattern 12 a are, as an example,each about 100 nm to about 4 μm (for example, 1 μm period). Note thatthe period in the X direction and the period in the Y direction of thegrating pattern 12 a may be different from each other. The gratingpattern 12 a may be produced, for example, as a hologram (for example,those obtained by printing interference fringes onto a photosensitiveresin). Alternatively, the grating pattern 12 a may be produced byforming grooves, etc., mechanically in a glass plate, etc., and bycoating the grooves, etc., with a reflective film. Furtheralternatively, the grating pattern surface 12 b may be covered by aprotective flat glass plate.

The laser light source 16 is composed, for example, of a He—Ne laser ora semiconductor laser, etc., and radiates, as an example, atwo-frequency heterodyne light composed of first and second linearlypolarized laser lights ML, RL of which frequencies are different fromeach other by a predetermined amount and of which polarizationdirections are orthogonal to each other. These laser lights are coherentwith each other (in a case that the polarization directions are made tobe parallel to each other); and the average wavelength of these laserlights is referred to as “λ”. The laser light source 16 supplies, to themeasurement calculation unit 42, a signal of reference frequency(reference signal) which is obtained by photo-electrically converting aninterference light formed or generated by interference between two lightbeams branched from these laser lights respectively. Note that it isalso allowable to use the homodyne interference system.

The optical fiber 17 is a double-core optical fiber of apolarization-preserving type which transmits the laser lights ML, RLemitted from the laser source 16 while maintaining respectivepolarization directions. In this embodiment, the first laser light MLemitted from the optical fiber 17 is a linearly polarized laser lightpolarized in the X direction parallel to the XY plane, and the secondlaser light RL emitted from the optical fiber 17 is a linearly polarizedlaser light polarized in the Z direction. The other optical fibers 39XA,39XB, 39YA, 39YB, and 39C are single-core fibers, and they can be any ofthe polarization-preserving type fibers and a normal type fibers.Further, a light-collecting lens may be provided at a light-incidentport of each of the other optical fibers 39XA, 39XB, 39YA, 39YB, and39C. In FIG. 1, the illustration of intermediate parts of the opticalfibers 17, 39XA, 39XB, 39YA, 39YB, and the like is omitted. It isallowable to use a beam-feeding optical system constructed of aplurality of mirrors instead of using the optical fiber 17, and/or it isallowable to directly receive the interference lights by thephotoelectric sensors 40XA, 40XB, 40YA, 40YB, and 40C without using theoptical fibers 39XA, 39XB, 39YA, 39YB, and 39C.

The detection head 14 includes a connection unit 18 having a lens 18 b(see FIG. 2C) which makes the laser lights ML, RL emitted from theoptical fiber 17 parallel light beams; a half prism 20A which dividesthe laser light ML emitted from the connection unit 18 into an X-axismeasuring light MX and a Y-axis measuring light MY and which divides thelaser light RL emitted from the connection unit 18 into an X-axisreference light RX and a Y-axis reference light RY; two mirrors 22A, 22Bwhich cause the measuring light MX and the reference light RX to comeinto the X-axis interferometer unit 15X substantially in the −Ydirection; and optical members 36A and 36B which cause greater parts ofthe measuring light MY and the reference light RY to come into theY-axis interferometer unit 15Y substantially in the +X direction. Inthis embodiment, the X-axis measuring light MX and the X-axis referencelight RX emitted from the half prism 20A are heterodyne beams which arerespectively linearly polarized in the X direction and the Z direction,and the Y-axis measuring light MY and the Y-axis reference light RYemitted from the half prism 20A are heterodyne beams which arerespectively linearly polarized in the Y direction and the Z direction.Each of the measuring lights MX, MY and the reference lights RX, RY hasa circular-shaped cross section (elliptical-shaped cross section, arectangular cross section, etc., are also allowable) which has adiameter of, for example, about 0.5 mm to several millimeters.

As depicted in FIG. 2C, the laser lights ML, RL are emitted from coreportions arranged adjacently in the optical fiber 17 and are convertedinto the parallel light beams by the lens 18 b. Thus, the laser lightsML, RL which have been converted into the parallel light beams intersectat a predetermined small angle β. Therefore, the measuring light MX andthe reference light RX emitted from the half prism 20A are relativelyinclined at the angle β, and further the measuring light MY and thereference light RY emitted from the half prism 20A are relativelyinclined at the angle β. By relatively inclining the measuring light MXand the reference light RX (measuring light MY and reference light RY),it is possible to reduce the noise light which would be otherwise mixedto a finally detected interference light(s).

In FIG. 1, a combining or synthesizing optical member 32X is fixed to anend surface in the −X direction of the support member 35X arranged onthe +Y direction side, via a combining or synthesizing optical member33X. The combining optical member 32X includes a half mirror surface A1and a polarized beam splitter surface (hereinafter referred to as “PBSsurface”) A2 which are parallel to a plane obtained by rotating the YZplane counterclockwise by 45 degrees with the axis parallel to the Zaxis as a rotation center. The combining optical member 33X includes aPBS surface A4 and a reflecting surface A3 which are parallel to a planeobtained by rotating the YZ plane clockwise by 45 degrees with the axisparallel to the Z axis as a rotation center. A wedge-shaped (cuneiform)prism 34X is fixed to a light-incident surface of the combining opticalmember 32X. Further, polarizing plates 41XA, 41XB are fixed to the endsurface in the +X direction of the support member 35X at positionsfacing the PBS surfaces A2 and A4, respectively. Light-incident ends ofthe optical fibers 39XA, 39XB are fixed to the polarizing plates 41XA,41XB, respectively.

In FIG. 1, an optical member 36A is fixed to the end portion in the +Ydirection of the end surface in the −X direction of the support member35Y arranged on the −Y direction side. The optical member 36A includes aPBS surface B2 and a beam splitter surface (hereinafter referred to as“BS surface”) B1 which has a high transmittance and a low reflectance.Further, combining optical members 33Y, 32Y which are constituted in thesame manner as the combining optical members 33X, 32X are fixed to anarea at the side of the −Y direction of the end surface in the −Xdirection of the support member 35Y, and a wedge-shaped (cuneiform)prism 34Y which has the same shape as the edge-shaped prism 34X is fixedto a light-incident surface of the combining optical member 32Y.Polarizing plates 41YB, 41YA, and 41C are fixed to the end surface inthe +X direction of the support member 35Y at positions facing the PBSsurfaces of the combining optical members 32Y, 33Y and the PBS surfaceB2 of the optical member 36A, respectively. Light-incident ends of theoptical fibers 39YB, 39YA, and 39C are fixed to the polarizing plates41YB, 41YA, and 41C respectively. The direction of crystal axis of eachof the polarizing plates 41XA, 41XB, 41YA, 41YB, and 41C is set to be anoblique direction so that the diffracted light or measuring light (to bedescribed later) which is linearly polarized in the Y direction andwhich is subjected to the measurement is combined with the referencelight linearly polarized in the Z direction to generate the interferencelight. The wedge-shaped prisms 34X, 34Y changes the traveling directionsof the incoming reference lights RX, RY to cancel out the angle βbetween the measuring light MX and the reference light RX and the angleβ between the measuring light MY and the reference light RY (see FIG.2C), thereby making the reference lights parallel to the diffractedlights to be measured.

The optical member 36B includes a BS surface B3 which has a lowtransmittance and a high reflectance, two reflecting surfaces B4, B5which are substantially orthogonal with each other, and a reflectingsurface B6 disposed at a position away from the BS surface B3 in the −Ydirection. Regarding the Y-axis measuring light MY and the Y-axisreference light RY which are branched by the half prism 20A, greaterparts thereof are transmitted through the BS surface B1 of the opticalmember 36A; a part of the measuring light MY and a part of the referencelight (reference light RY3) reflected by the BS surface B1 come into thePBS surface B2; and the S-polarized reference light RY3 is reflected bythe PBS surface B2. Regarding the measuring light MY and the referencelight RY transmitted through the BS surface B1, greater parts thereofare reflected by the BS surface B3 of the optical member 36B, and thereflected measuring light MY and reference light RY come into the Y-axisinterferometer unit 15Y substantially from the −X direction via thereflecting surface B6.

A part of the measuring light (measuring light MY3) and a part of thereference light RY transmitted through the BS surface B3 are reflectedby the reflecting surfaces B4, B5 to come into the PBS surface B2 of theoptical member 36A, and the P-polarized measuring light MY3 istransmitted through the PBS surface B2 and is combined with thereference light RY3 reflected by the PBS surface B2, thereby forming theinterference light for comparison or reference. The interference lightfor comparison comes into the optical fiber 39C via the polarizing plate41C, and the interference light delivered by the optical fiber 39C isreceived by the photoelectric sensor 40C. As an example, the positionand the angle of reflecting surface B5 of the optical member 36B areset, as an example, to adjust the position and the angle of themeasuring light MY3, so that the measuring light MY3 and the referencelight RY3 combined by the PBS surface B2 are coaxial and parallel toeach other.

The X-axis interferometer unit 15X includes a polarized beam splittermember (hereinafter referred to as “PBS member”) 24X, a pair of roofprisms 26XA, 26XB, a pair of large-size reflecting members 28XA, 28XB ofa right-angle prism type, and a pair of small-size reflecting members30XA, 30XB of a right-angle prism type. The PBS member 24X has apolarized beam splitter surface (hereinafter referred to as “PBSsurface”) A11 (see FIG. 2A) into which the measuring light MX and thereference light RX reflected substantially in the −Y direction by themirror 22B come. The pair of roof prisms 26XA, 26XB is symmetricallyfixed to sandwich the PBS member 24X in the X direction. The pair ofreflecting members 28XA, 28XB is fixed on the upper surface of the PBSmember 24X at the side of the +Y direction symmetrically in the Xdirection to face the outside. The pair of reflecting members 30XA, 30XBis fixed on the upper surface of the PBS member 24X at the side of the−Y direction symmetrically in the X direction to face the outside. TheX-axis interferometer unit 15X further includes a reflecting member 22C,the wedge-shaped prism 34X, and the combining optical members 32X, 33X.

A first reflecting unit 25XA is constructed of the roof prism 26XA andthe reflecting members 28XA, 30XA at the side of the +X direction. Asecond reflecting unit 25XB is constructed of the roof prism 26XB andthe reflecting members 28XB, 30XB at the side of the −X direction.Opening(s) (not depicted) for allowing the measuring light MX and thediffracted light emitted from the diffraction grating 12 to pass is/areformed in the second member 7, and the PBS member 24 is fixed to thesecond member 7 to cover the opening(s) therewith.

FIG. 2A depicts the PBS member 24X and the reflecting units 25XA, 25XBof the interferometer unit 15X in FIG. 1. In FIG. 2A, the PBS member 24Xis a member having a double-layered structure as follows. That is, theinterior of a part, defined at the side of the +Y direction, to whichthe large-size reflecting members 28XA, 28XB are fixed is a transmittingpart, and in the interior of a part, defined at the side of the −Ydirection, to which the small-size reflecting members 30XA, 30XB arefixed, the PBS surface A11 is obliquely formed (in a state of beinginclined at 45 degrees to the XY surface around the X axis). The PBSmember 24X has a rectangular parallelepiped shape surrounded by sixsurfaces of two surfaces parallel to the XY plane, two surfaces parallelto the YZ plane, and two surfaces parallel to the ZX plane. The PBSmember 24X, however, may have other shapes. The roof prism 26XA of thereflecting unit 25XA includes a light-incident surface A12, a pair ofreflecting surfaces A13, A14, and a light-exit surface A15. Thelight-incident surface A12 is inclined counterclockwise to the bottomsurface of the PBS member 24X by an angle α1 (see FIG. 3A). The pair ofreflecting surfaces A13, A14 is formed by arranging the reflectingsurfaces A13 and A14 symmetrical with respect to a ridge line A16parallel to the XZ plane and orthogonal to each other. The light-exitsurface A15 is brought in tight contact with the PBS member 24X and thereflecting members 28XA, 30XA. The ridge line A16 of the roof prism 26XAis inclined counterclockwise to the ZY plane by an angle α2 (see FIG.3A). The other roof prism 26XB has a shape symmetrical to the roof prism26XA. The roof prism 26XB also includes two reflecting surfaces A23, A24which are orthogonal to each other.

The S-polarized measuring light MX and the P-polarized reference lightRX reflected by the mirror 22B in FIG. 1 come into the PBS surface A11of the PBS member 24X of FIG. 2A substantially from the +Y direction.The reference light RX is transmitted through the PBS surface A11 and isemitted from the PBS member 24 substantially in the −Y direction.Meanwhile, the S-polarized measuring light MX is reflected by the PBSsurface A11 to come into the grating pattern surface 12 b (gratingpattern 12 a) of the diffraction grating 12X perpendicularly(substantially parallel to the Z axis). The term “to come into (thegrating pattern surface 12 b) perpendicularly” herein means includingnot only a case that the measuring light MX is caused to come into thegrating pattern surface 12 b perpendicularly, but also a case that themeasuring light MX is caused to come substantially perpendicularly intothe grating pattern surface 12 b while being inclined, for example, atabout 0.5 degree to about 1.5 degrees, with respect to an axis parallelto the Z axis, in the X direction (θy direction) and/or in the Ydirection (θx direction) for the purpose of lowering the effect orinfluence brought about by the 0-order light (regular reflection light).

In this embodiment, there are generated ±1st order diffracted lights DX1and DX2, which are symmetric in the X direction, via diffraction of themeasuring light MX coming substantially perpendicularly into the gratingpattern surface 12 b of the diffraction grating 12. The generateddiffracted light DX1 comes into a light-incident surface of the roofprism 26XA, and the generated diffracted light DX2 comes into alight-incident surface of the roof prism 26XB. In this situation, ±1storder diffracted lights are also generated symmetrically in the Ydirection, but the diffracted lights in the Y direction are not used inthe X-axis interferometer unit 15X. The +1st order diffracted light DX1shifts in the +Y direction via the light-incident surface A12 and thereflecting surfaces A13, A14 of the roof prism 26XA, and travels in the−X direction parallel to the X axis to come into the reflecting member28XA via the light-exit surface A15. Then, the diffracted light DX1reflected by the reflecting member 28XA is transmitted through the PBSmember 24X to come substantially perpendicularly into the gratingpattern surface 12 b of the diffraction grating 12. Symmetrical to the+1st order diffracted light DX1, the −1st order diffracted light DX2shifts in the +Y direction via the reflecting surfaces A23, A24, etc.,of the roof prism 26XB, and travels in the +X direction parallel to theX axis to come into the reflecting member 28XB. Then, the diffractedlight DX2 reflected by the reflecting member 28XB comes substantiallyperpendicularly into the grating pattern 12 a of the diffraction grating12.

As depicted in FIG. 2B, positions, in the grating pattern 12 a, intowhich the diffracted lights DX1, DX2 come are each shifted from theposition, in the grating pattern 12 a, into which the measuring light MXcomes by a spacing distance a1 in the Y direction and a spacing distancea2 in the X direction. Shifts, in the X direction, of the positions intowhich the diffracted lights DX1, DX2 come are symmetric with respect tothe measuring light MX. The distance a1 is approximately ½ of the widthof the PBS member 24X in the Y direction, and the distance a2 isapproximately ⅓ of the width of the PBS member 24X in the X direction.By allowing the measuring light MX and the diffracted lights DX1, DX2 tocome into the diffraction grating 12 in accordance with the abovearrangement, it is possible to downsize the structure of theinterferometer unit 15X. Noted that each of the spacing distances a1, a2may be any spacing distance. Further, the positions into which themeasuring light MX and the diffracted lights DX1, DX2 come may be set inaccordance with any arrangement.

There are generated +1st order diffracted light EX1 (double-diffractedlight) and −1st order diffracted light EX2 (double-diffracted light) viadiffraction of the diffracted lights DX1, DX2 reflected by thereflecting members 28XA, 28XB respectively, from the diffraction grating12 symmetrically in the X direction. The diffracted light EX1 shifts inthe −Y direction by being reflected by the light-incident surface A12and the reflecting surfaces A14, A13 of the roof prism 26XA in thisorder, and travels in the −X direction parallel to the X axis to comeinto the reflecting member 30XA. The S-polarized diffracted light EX1reflected by the reflecting member 30XA is reflected by the PBS surfaceA11 of the PBS member 24X and is emitted from the PBS member 24Xsubstantially in the −Y direction. Symmetrical to the diffracted lightEX1, the diffracted light EX2 shifts in the −Y direction by beingreflected by the light-incident surface and the reflecting surfaces A24,A23 of the roof prism 26XB in this order, and travels in the +Xdirection parallel to the X axis to come into the reflecting member30XB. Then, the S-polarized diffracted light EX2 reflected by thereflecting member 30XB is reflected by the PBS surface A11 and isemitted from the PBS member 24X substantially in the −Y direction.

In FIG. 1, the diffracted lights EX1, EX2 emitted from the PBS member24X are reflected by the reflecting member 22C, and the reflecteddiffracted lights EX1, EX2 are transmitted through the PBS surfaces A2,A4 of the combining optical members 32X, 33X, respectively. The reasonthereof is that although each of the diffracted lights EX1, EX2 has theS-polarization to the PBS surface A11 of the PBS member 24X, each of thediffracted lights EX1, EX2 has the P-polarization to one of the PBSsurfaces A2, A4. The reference light RX transmitted through the PBSmember 24X is reflected by the reflecting member 22C to come into thehalf mirror surface A1 of the combining optical member 32X via thewedge-shaped prism 34X. A reference light RX1 reflected by the halfmirror surface A1 is reflected by the PBS surface A2 and then iscoaxially combined with the diffracted light EX1, thereby forming theinterference light. This interference light is received by thephotoelectric sensor 40XA via the polarizing plate 41XA and the opticalfiber 39XA. A reference light RX2 transmitted through the half mirrorsurface A1 is reflected by the reflecting surface A3 of the combiningoptical member 33X. After that, the reflected reference light RX2 isreflected by the PBS surface A4 and then is coaxially combined with thediffracted light EX2, thereby forming the interference light. Thisinterference light is received by the photoelectric sensor 40XB via thepolarizing plate 41XB and the optical fiber 39XB. The reason thereof isthat although each of the reference lights RX1, RX2 has theP-polarization to the PBS surface A11 of the PBS member 24X, each of thereference lights RX1, RX2 has the S-polarization to one of the PBSsurfaces A2, A4.

The Y-axis interferometer unit 15Y includes a PBS member 24Y andreflecting units 25YA, 25YB those of which are configured by integrallyrotating the PBS member 24X and the reflecting units 25XA, 25XB of theX-axis interferometer unit 15X by 90 degrees. That is, the reflectingunits 25YA, 25YB also include roof prisms 26YA, 26YB, large-sizereflecting members 28YA, 28YB, and small-size reflecting members 30YA,30YB, respectively. The PBS member 24Y is fixed to the second member 7to cover opening(s) (not depicted) therewith. The interferometer unit15Y further includes the wedge-shaped prism 34Y and the combining orsynthesizing optical members 32Y, 33Y.

The measuring light MY and reference light RY reflected by thereflecting surface B6 come into the PBS member 24Y of the Y-axisinterferometer unit 15Y. The P-polarized reference light RY istransmitted through the PBS surface of the PBS member 24Y and is emittedin the +X direction. The S-polarized measuring light MY is reflected bythe PBS surface of the PBS member 24Y to come substantiallyperpendicularly into the grating pattern 12 a of the diffraction grating12, which generates, from the grating pattern 12 a, ±1st orderdiffracted lights DY1, DY2 (see FIG. 3B) which are symmetric in the Ydirection. The ±1st order diffracted light generated in the X directionare not used in the interferometer unit 15Y. The diffracted light DY1(DY2) comes substantially perpendicularly into the grating pattern 12 aof the diffraction grating 12 via the reflecting unit 25YA (reflectingunit 25YB). Then, +1st order diffracted light EY1 in the Y directiongenerated via diffraction of the diffracted light DY1 and −1st orderdiffracted light EY2 in the Y direction generated via diffraction of thediffracted light DY2 are generated from the diffraction grating 12. Thediffracted light EY1 travels through the reflecting unit 25YA, isreflected by the PBS surface of the PBS member 24Y and is emitted in the+X direction. The diffracted light EY2 travels through the reflectingunit 25YB, is reflected by the PBS surface of the PBS member 24Y and isemitted in the +X direction.

The P-polarized diffracted lights EY1, EY2 emitted from the PBS member24Y are transmitted through the PBS surfaces of the combining opticalmembers 33Y, 32Y, respectively. The reference light RY transmittedthrough the PBS member 24Y comes into a half mirror surface of thecombining optical member 32Y via the wedge-shaped prism 34Y. A referencelight RY2 reflected by the half mirror surface is reflected by the PBSsurface and then is coaxially combined with the diffracted light EY2,thereby forming the interference light. This interference light isreceived by the photoelectric sensor 40YB via the polarizing plate 41YBand the optical fiber 39YB. A reference light RY1 transmitted throughthe half mirror surface is reflected by the reflecting surface of thecombining optical member 33Y. After that, the reflected reference lightRY1 is reflected by the PBS surface and then is coaxially combined withthe diffracted light EY1, thereby forming the interference light. Thisinterference light is received by the photoelectric sensor 40YA via thepolarizing plate 41YA and the optical fiber 39YA.

In FIG. 1, the measurement calculation unit 42 has a first calculationunit 42X, a second calculation unit 42Y and a third calculation unit42T. The X-axis photoelectric sensor 40XA supplies a detection signal(photo-electric conversion signal) of an interference light generated byinterference between the diffracted light EX1 and the reference lightRX1 to the first calculation unit 42X, and the X-axis photoelectricsensor 40XB supplies a detection signal of an interference lightgenerated by interference between the diffracted light EX2 and thereference light RX2 to the first calculation unit 42X. Further, theY-axis photoelectric sensor 40YA supplies a detection signal of aninterference light generated by interference between the diffractedlight EY1 and the reference light RY1 to the second calculation unit42Y, and the Y-axis photoelectric sensor 40YB supplies a detectionsignal of an interference light generated by interference between thediffracted light EY2 and the reference light RY2 to the secondcalculation unit 42Y. A signal of the reference frequency (referencesignal) from the laser light source 16 and a signal (comparison signal)of the interference light for comparison, detected by the photoelectricsensor 40C, having substantially the reference frequency are supplied tothe first calculation unit 42X and the second calculation unit 42Y.

Here, relative moving amounts (relative displacement) of the secondmember 7 relative to the first member 6 in the X, Y and Z directions arereferred to as “X”, “Y” and “Z”, respectively; and relative movingamounts in the Z direction obtained in the first calculation unit 42Xand the second calculation unit 42Y are referred to as “ZX” and “ZY”,respectively. In this case, as an example, the first calculation unit42X obtains a first relative moving amount (a·X+b·ZX) in the X and Zdirections from the detection signal and the reference signal (orcomparison signal) of the photoelectric sensor 40XA by using previouslyknown coefficients “a” and “b”; the first calculation unit 42X obtains asecond relative moving amount (−a·X+b·ZX) in the X and Z directions fromthe detection signal and the reference signal (or comparison signal) ofthe photoelectric sensor 40XB; the first calculation unit 42X obtains aX-direction relative moving amount (X) and a Z-direction relative movingamount (ZX) from the first and second relative moving amounts; and thenthe first calculation unit 42X supplies the calculation results to thethird calculation unit 42T. The second calculation unit 42Y obtains afirst relative moving amount (a·Y+b·ZY) in the Y and Z directions fromthe detection signal and the reference signal (or comparison signal) ofthe photoelectric sensor 40YA; the second calculation unit 42Y obtains asecond relative moving amount (−a·Y+b·ZX) in the Y and Z directions fromthe detection signal and the reference signal (or comparison signal) ofthe photoelectric sensor 40YB; the second calculation unit 42Y obtains aY-direction relative moving amount (Y) and a Z-direction relative movingamount (ZY) from the first and second relative moving amounts; and thenthe second calculation unit 42Y supplies the calculation results to thethird calculation unit 42T.

The third calculation unit 42T outputs, as the relative moving amountsof the second member 7 relative to the first member 6 in the X and Ydirections, values obtained by correcting the relative moving amount (X)and the relative moving amount (Y), which are supplied from the firstand second calculation units 42X and 42Y respectively, by predeterminedoffsets. Further, as an example, the third calculation unit 42T outputs,as the relative moving amount of the second member 7 relative to thefirst member 6 in the Z direction, a value obtained by correcting anaverage value (=(ZX+ZY)/2) of the relative moving amount (ZX) and therelative moving amount (ZY) in the Z direction, which are supplied fromthe first and second calculation units 42X and 42Y respectively, by apredetermined offset. The detection resolving powers of the relativemoving amounts in the X, Y and Z directions are, for example, about 0.5nm to about 0.1 nm. Since the optical paths of the measuring lights MX,MY, etc. are short in the encoder 10, it is possible to reduce theshort-term change (variation) of the measured value due to thetemperature fluctuation of the air on the optical path. Further, sincethe interference light generated by interference between the +1st orderdiffracted lights EX1 and EY1 which are double diffracted lights and thereference lights RX1 and RY1 corresponding to the +1st order diffractedlights EX1 and EY1 and the interference light generated by interferencebetween the −1st order diffracted lights EX2 and EY2 which are doublediffracted lights and the reference lights RX2 and RY2 corresponding tothe −1st order diffracted lights EX2 and EY2 are finally detected, thedetection resolving power (detection precision) of the relative movementamount can be improved (miniaturized) to ½. Furthermore, by using the±1st order diffracted lights, it is possible to reduce any measurementerror due to the relative rotational angle between the first member 6and the second member 7 in the Oz direction.

Next, the optical path of the diffracted light of the detection head 14of the embodiment will be explained in detail. FIG. 3A depicts maincomponents or parts of the X-axis interferometer unit 15X and thediffraction grating 12. In FIG. 3A, when the measuring light MX comesperpendicularly into the grating pattern 12 a of the diffraction grating12 (when the measuring light comes into the grating pattern 12 a inparallel to the Z axis), a diffraction angle ϕx of the +1st orderdiffracted light DX1 in the X-direction brought about by the measuringlight MX satisfies the following relation using the period p of thegrating pattern 12 a and the wavelength λ of the measuring light MX. Atthis time, a diffraction angle of the −1st order diffracted light DX2 inthe X direction brought about by the measuring light MX is −ϕx.p·sin(ϕx)=λ  (1)

As an example, provided that the period p is 1,000 nm (1 μm) and thewavelength λ of the measuring light MX is 633 nm, then the diffractionangle ϕX is approximately 39 degrees. Further, the diffracted light DX1is bent by the roof prism 26XA (light-incident surface A12 andreflecting surfaces A13, A14) and the reflecting member 28XA to beparallel to the measuring light MX (here, parallel to the Z axis), andthe diffracted light DX1 comes again into the diffraction grating 12.Therefore, the angle α1 of the light-incident surface A12 of the roofprism 26XA, the angle α2 of the ridge line A16, a refractive index ng,and an incident angle i (function of the angle α1 and the diffractionangle ϕX) of the diffracted light DX1 with respect to the light-incidentsurface A12 are preferably set so that the diffracted light DX1reflected by the reflecting member 28XA is substantially parallel to theZ axis.

Further, in this embodiment, it is preferable that a rate of change(dδ/di) of a deflection angle δ of the diffracted light DX1 coming intothe light-incident surface A12 of the roof prism 26XA with respect tothe incident angle i is set to be cos(ϕx), as indicated below.dδ/di=cos(ϕx)=cos {arcsin(λ/p)}  (3)

The condition which is defined by this formula (3) means that the rateof change (dδ/di) of the deflection angle δ at the light-incidentsurface A12 cancels out the rate of change in the diffraction angle ofthe diffracted light DX1 brought about when the incident angle of themeasuring light MX with respect to the diffraction grating 12 is changedfrom 0 (zero) (to be described in detail later on).

In a case that the measuring light MX comes perpendicularly into thegrating pattern 12 a (in a case that the measuring light comes into thegrating pattern 12 a in parallel to the Z axis), the diffracted lightDX1 reflected by the reflecting unit 25XA comes perpendicularly into thegrating pattern 12 a at a position shifted in the +X direction and the+Y direction from the position where the measuring light MX came intothe grating pattern 12 a (see FIG. 2B). The diffraction angle of the+1st order diffracted light EX1 generated, via diffraction of thediffracted light DX1, from the grating pattern 12 a is same as “ϕx” ofthe formula (1); and the optical path of the diffracted light EX1 isbent by the reflecting unit 25XA to be parallel to the Z axis and the+1st order diffracted light EX1 travels toward the PBS surface A11 ofthe PBS member 24. At this time, the −1st order diffracted light DX2from the diffraction grating 12 brought about by the measuring light MXcomes perpendicularly into the grating pattern 12 a, via the reflectingunit 25X, at a position shifted in the −X direction and the +Y directionfrom the position where the measuring light MX came into the gratingpattern 12 a symmetrically to the diffracted light DX1 (see FIG. 2B).Further, the optical path of the −1st order diffracted light EX2generated, via diffraction of the diffracted light DX2, from thediffraction grating 12 is bent by the reflecting unit 25XB to beparallel to the Z axis and the −1st order diffracted light EX2 travelstoward the PBS surface A11.

FIG. 3B depicts main components or parts of the Y-axis interferometerunit 15Y and the diffraction grating 12. In FIG. 3B, when the measuringlight MY comes perpendicularly into the grating pattern 12 a of thediffraction grating 12, the diffraction angle ϕy of the +1st orderdiffracted light DY1 in the Y direction brought about by the measuringlight MY is same as the diffraction angle “ϕx” in the X direction of theformula (1). The diffracted light DY1 reflected by the reflecting unit25YA comes perpendicularly into the grating pattern 12 a at a positionshifted in the −X direction and the +Y direction from the position wherethe measuring light MY came into the grating pattern 12 a. Meanwhile,the diffracted light DY2 reflected by the reflecting unit 25YB comesperpendicularly into the grating pattern 12 a at a position shifted inthe −X direction and the −Y direction from the position where themeasuring light MY came into the grating pattern 12 a. The optical pathof +1st order diffracted light EY1 generated, via diffraction of thediffracted light DY1 traveled through the reflecting unit 25YA, from thediffraction grating 12 and the optical path of −1st order diffractedlight EY2 generated, via diffraction of the −1st order diffracted lightDY2 in the Y direction brought about by the measuring light MY, from thediffraction grating 12 are respectively bent by the reflecting units25YA, 25YB to be parallel to the Z axis; and the ±1st order diffractedlights EY1 and EY2 travel toward the PBS surface of the PBS member 24Y.

Further, the following case is assumed that in the arrangement depictedin FIG. 3A, the relative position in the Z direction of the gratingpattern surface 12 b of the diffraction grating 12 is changed relativeto the interferometer unit 15X by 6Z to a position B11, as depicted inFIG. 4A. In this case, the +1st order diffracted light DX1 brought aboutby the measuring light MX comes into the reflecting unit 25XA in a statethat the optical path of the +1st order diffracted light DX1 isparallelly shifted to a position B12. In the reflecting unit 25XA, theoptical path of the exiting light is shifted symmetrically to the shiftof the optical path of the incoming light about the center (ridge lineA16). Thus, the diffracted light DX1 reflected by the reflecting unit25XA comes into the diffraction grating 12 at a position where thegrating pattern surface 12 b, of which position has been changed to theposition B11, crosses the optical path of the +1st order diffractedlight EX1 which is provided under the condition that the relativeposition in the Z direction of the grating pattern surface 12 b is notchanged. Accordingly, even when the grating pattern surface 12 b ischanged or shifted to the position B11, an optical path B13 of the +1storder diffracted light EX1 generated, via diffraction of the diffractedlight DX1, from the diffraction grating 12 is same as the optical pathof the +1st order diffracted light EX1 obtained when the relativeposition in the Z direction of the grating pattern surface 12 b is notchanged. Therefore, when the diffracted light EX1 and the referencelight RX1 are coaxially combined in the PBS surface A2 (see FIG. 1) togenerate the interference light, there is not any relative lateral shiftamount between the diffracted light EX1 and the reference light RX1; andthus there is no lowering of the ratio of alternating current signal(beat signal or signal component) of the detection signal which isobtained when the interference light is photo-electrically converted.

This is same also with the −1st order diffracted light DX2 in the X axisand ±1st order diffracted lights DY1 and DY2 in the Y axis; even whenthe relative position of the grating pattern surface 12 b in the Zdirection is changed, the ratios of the beat signals of the detectionsignals of the photoelectric sensors 40XA to 40YB depicted in FIG. 1 arenot lowered. Accordingly, it is possible to measure the relative movingamount between the second member 7 and the first member 6 by using thedetection signals with a high S/N ratio and high precision.

Next, the following case is assumed that in the arrangement depicted inFIG. 3A, the grating pattern surface 12 b of the diffraction grating 12is changed relative to the X-axis interferometer unit 15Xcounterclockwise about an axis parallel to the Y axis by an angle ε, asdepicted in FIG. 4B. In this case, provided that the incident angle ofthe measuring light MX with respect to the grating pattern surface 12 bis 6, and that the diffraction angle of the +1st order diffracted lightDX1 is (ϕx+δϕx), the following relation holds.sin(ϕx+δϕx)−sin ε=λ/p  (4)

In this case, when ε and δϕx are minute amounts, sin(ϕx) differentiatedis cos(ϕx), and thus the formula (4) is as follows.sin(ϕx)+cos(ϕx)·δϕx−ε=λ/p  (5)

In the formula (5), considering that “sin(ϕx)” is “λ/p” from the formula(1), the following formula is obtained.δϕx=ε/cos(ϕx)  (6)

Further, an amount of change δϕ of the angle of an optical path B22, ofthe +1st order diffracted light DX1 from the diffraction grating 12 whenthe grating pattern surface 12 b is inclined by the angle ε, is asfollows.δϕ={1+1/cos(ϕx)}ε  (7)

Furthermore, since the rate of change (dδ/di) of the deflection angle δwith respect to the incident angle i at the light-incident surface A12of the roof prism 26XA is cos(ϕx) as indicated in the formula (3), anamount of change δε1 of the angle of an optical path B23 of thediffracted light DX1 transmitted through the roof prism 26XA is asfollows:δε1=δϕ·cos(ϕx)={cos(ϕx)+1}ε  (8)

Moreover, since the grating pattern surface 12 b is inclined by theangle ε, an incident angle δε of the diffracted light DX1 coming intothe grating pattern surface 12 b from the reflecting unit 25XA is asfollows.δε=ε·cos(ϕx)  (9)

When the diffracted light DX1 comes into the diffraction grating 12again with the incident angle δε, an amount of change δϕ1 of thediffraction angle of the +1st order diffracted light EX1 (doublediffracted light) from the diffraction grating 12 brought about by thediffracted light DX1 is as follows from the formula (6).δϕ1=ε  (10)

This means that the amount of change δϕ1 of the diffraction angle of thediffracted light EX1 is same as the inclination angle ε of the gratingpattern surface 12 b, namely that an optical path B24 of the diffractedlight EX1 is parallel to the optical path before the grating patternsurface 12 b is inclined. Further, any lateral shift of the optical pathB24 of the diffracted light EX1 does not occur. Accordingly, when thediffracted light EX1 and the reference light RX1 are coaxially combinedin the PBS surface A2 to generate the interference light, there are notany relative inclination shift amount and any relative lateral shiftamount between the diffracted light EX1 and the reference light RX1; andthus there is no lowering of the ratio of alternating current signal(beat signal or signal component) of the detection signal which isobtained when the interference light is photo-electrically converted.This is same also with the −1st order diffracted light EX2 of the Xaxis.

Further, also in a case that the grating pattern 12 b of the diffractiongrating 12 is inclined about an axis parallel to the X axis, there arenot generated any shift in the inclination angle of the optical path andany lateral shift of the optical path of each of the ±1st orderdiffracted lights EY1 and EY2 of the Y axis as well. Accordingly, theratios of the beat signals of the detection signals of the photoelectricsensors 40XA to 40YB depicted in FIG. 1 are not lowered. Thus, it ispossible to measure the relative moving amount of the second member 7relative to the first member 6 by using the detection signals with ahigh S/N ratio and high precision. Note that in a case that the gratingpattern surface 12 b of the diffraction grating 12 is inclined about anaxis parallel to the X axis (or the Y axis), the detection signals ofthe X axis (or the detection signals of the Y axis) are notsubstantially affected.

In the foregoing explanation, it is assumed that the diffraction grating12 side is inclined to the detection head 14 (interferometer units 15X,15Y). However, also in a case that the incident angle of each of themeasuring lights MX, MY with respect to the diffraction grating 12 ischanged from 0 (zero) by a minute amount in the X direction and/or the Ydirection, there is not any inclination and lateral shift of the opticalpath of each of the diffracted lights EX1, EX2, EY1 and EY2 as well.Thus, it is possible to measure the relative moving amount between thesecond member 7 and the first member 6 with a high S/N ratio and highprecision.

The effects, etc. of the embodiment are as follows.

The encoder 10 of the embodiment is a three-axis encoder which measuresthe relative moving amount of the second member 7 movable relative tothe first member 6 three-dimensionally in the X, Y and Z directions.Further, the encoder 10 is provided with the reflective-type diffractiongrating 12 which is provided on the first member 6 and which has thetwo-dimensional grating pattern 12 a of which periodic directions arethe X and Y directions; the laser light source 16 which generates alaser light including the measuring light MX and the reference light RX;the PBS member 24X (first optical member) which is provided on thesecond member 7 and which causes the measuring light MX to betransmitted therethrough so that the measuring light MX comessubstantially perpendicularly into the grating pattern surface 12 b ofthe diffraction grating 12; the reflecting unit 25XA which is providedon the second member 7, which causes the +1st order diffracted light DX1(first diffracted light) in the X direction generated via diffraction ofthe measuring light MX, from the diffraction grating 12, to come intothe diffraction grating 12, and which causes the +1st order diffractedlight EX1 (second diffracted light) in the X direction generated, viadiffraction of the +1st order diffracted light DX1, from the diffractiongrating 12 to come into the PBS member 24X; the reflecting unit 25XBwhich is provided on the second member 7, which causes the −1st orderdiffracted light DX2 (third diffracted light) generated via diffractionof the measuring light MX, from the diffraction grating 12,symmetrically to the diffracted light DX1 in the X direction to comeinto the diffraction grating 12, and which causes the −1st orderdiffracted light EX2 (fourth diffracted light) in the X directiongenerated, via diffraction of the −1st order diffracted light DX2, fromthe diffraction grating 12 to come into the PBS member 24X; thephotoelectric sensors 40XA, 40XB which respectively detect interferencelights generated by interference between reference lights branched fromthe reference light RX and the diffracted lights EX1 and EX2 reflectedby the PBS member 24X; and the measurement calculation unit 42(measuring unit) which measures the relative moving amounts in the Xdirection and the Z direction of the second member 7 relative to thefirst member 6 by using detection signals of the photoelectric sensors40XA, 40XB.

As indicated in the flowchart of FIG. 12, the measurement method usingthe encoder 10 is a method for measuring the relative moving amountbetween the second member 7 and the first member 6, and includes a step302 in which the measuring light MX is allowed to come substantiallyperpendicularly into the grating pattern surface 12 b of thereflective-type diffraction grating 12 provided on the first member 6and having the grating pattern 12 a of which periodic directions are theX direction and the Y direction, via the PBS member 24X provided on thesecond member 7; a step 304 in which the +1st diffracted light DX1 inthe X direction generated, via diffraction of the measuring light MX,from the diffraction grating 12, is allowed to come into the diffractiongrating 12 via the reflecting unit 25XA provided on the second member 7,and the +1st order diffracted light EX1 generated, via diffraction ofthe diffracted light DX1, from the diffraction grating 12 is allowed tocome into the PBS member 24X; a step 306 in which the −1st diffractedlight DX2 in the X direction generated via diffraction of the measuringlight MX, from the diffraction grating 12, is allowed to come into thediffraction grating 12 via the reflecting unit 25XB provided on thesecond member 7, and the −1st order diffracted light EX2 generated, viadiffraction of the diffracted light DX2, from the diffraction grating 12is allowed to come into the PBS member 24X; and a step 308 in which theinterference lights generated by interference between the referencelights RX1, RX2 and the diffracted lights EX1, EX2 via the PBS member24X are respectively detected, and the relative moving amount betweenthe second member 7 and the first member 6 is obtained based on thedetection results.

According to this embodiment, the incident angle of each of thediffracted lights DX1, DX2 when coming into the diffraction grating 12is made to be substantially 0 (zero) by each of the reflecting units25XA, 25XB. Therefore, even when the relative position between the firstmember 6 and the second member 7 is changed and consequently therelative height (position in the Z direction) of the grating patternsurface 12 b of the diffraction grating 12 relative to the PBS member24X (detection head 14) is changed, there is not any substantialvariation or fluctuation in the optical path of each of the diffractedlights EX1, EX2 (double diffracted light) from the diffraction grating12 brought about by each of the diffracted lights DX1, DX2, and therelative shift amount in the lateral direction between the diffractedlight EX1 and the reference light RX1 and the relative shift amount inthe lateral direction between the diffracted light EX2 and the referencelight RX2 are each substantially 0 (zero). Accordingly, there is nolowering of the intensity of the beat signal (signal including thepositional information) of the interference light with respect to thechange in the height of the grating pattern surface 12 b of thediffraction grating 12, thereby making it possible to maintain highmeasurement precision or accuracy of the relative moving amount of thesecond member 7 relative to the first member 6. On the other hand, ifthe relative positions in the X and Y directions between the firstmember 6 and the second member 7 are fixed, it is possible to measurethe relative moving amount in the Z direction of the second member 7relative to the first member 6 from the detection signal of thephotoelectric sensor 40XA.

The encoder 10 further includes reflecting units 25YA, 25YB each ofwhich causes one of the ±1st order diffracted lights DY1, DY2 to comeinto the diffraction grating 12 at the incident angle of substantially 0(zero), the ±1st order diffracted lights DY1, DY2 being generated, viadiffraction of the measuring light MY coming substantiallyperpendicularly into the diffraction grating 12 via the PBS member 24Y,from the diffraction grating 12 in the Y direction; and thephotoelectric sensors 40YA, 40YB which respectively detect interferencelights generated by interference between the reference lights RY1, RY2and the ±1st order diffracted lights EY1, EY2 generated, via diffractionof the diffracted lights DY1, DY2, from the diffraction grating 12.Therefore, even when the relative height of the grating pattern surface12 b of the diffraction grating 12 is changed, it is possible to measurethe relative moving amount in the Y direction of the second member 7relative to the first member 6 from the detection signals of thephotoelectric sensors 40YA, 40YB with high precision.

The following modifications may be made to the embodiment describedabove.

Although the two-dimensional diffraction grating 12 is used in theembodiment described above, it is allowable to use a one-dimensionaldiffraction grating which has the periodicity, for example, only in theX direction, instead of using the diffraction grating 12. In this case,it is allowable to omit the Y-axis interferometer unit 15Y, thephotoelectric sensors 40YA, 40YB, and the like from the detection head14; in this case, it is possible to measure the relative moving amountsin the X and Z directions between the first member 6 and the secondmember 7 by using the detection signals of the photoelectric sensors40XA and 40XB.

In the embodiment, the interference lights generated by interferencebetween the diffracted lights EX1, EX2, EY1 and EY2 and the referencelights RX1, RX2, RY1 and RY2, respectively, are detected. It isallowable, however, to detect for example an interference lightgenerated by interference between a X-axis +1st order diffracted lightEX1 of a measuring light having a first frequency and a X-axis −1storder diffracted light EX2 of a measuring light having a secondfrequency (the light used in the embodiment as the reference light), andto detect an interference light generated by interference between aY-axis +1st order diffracted light EY1 of the measuring light having thefirst frequency and a Y-axis −1st order diffracted light EY2 of themeasuring light having the second frequency. In this case, it ispossible to measure the relative moving amounts between the first member6 and the second member 7 in the X and Y directions, and to perform themeasurement always with a high S/N ratio and high precision, since thereis no lateral shift between the two diffracted lights even when therelative height of the grating pattern surface 12 b of the diffractiongrating 12 is changed or varied.

Subsequently, in the above embodiment, the diffracted lights DX1, EX1generated from the diffraction grating 12 come into the reflectingmembers 28XA, 30XA respectively via the roof prism 26XA. However, asdepicted in the main components of an X-axis interferometer unit 15XA ofa first modification in FIG. 5A, it is allowable to use a roof mirror44XA (see FIG. 5B) having reflecting surfaces A33, A34 which areorthogonal to each other and a wedge-shaped (cuneiform) prism 46XAhaving a vertical angle (apical angle) a3, instead of the roof prism26XA. In this case, it is allowable to use a roof mirror 44XB and awedge-shaped (cuneiform) prism 46XB instead of the roof prism 26XB. Theuse of the roof mirrors 44XA, 44XB may reduce weight of the X-axisinterferometer unit 15XA. The wedge-shaped prisms 46XA, 46XB may beomitted. Similarly, planer mirrors may be used as the reflecting members28XA, 30XA, etc.

As depicted in an X-axis interferometer unit 15XB of a secondmodification in FIG. 6, ½ wavelength plates 38XA, 38XB for adjusting thepolarization directions of the +1st diffracted lights DX1, EX1 may beprovided in the optical paths of the diffracted lights DX1, EX1travelling from the diffraction grating 12 toward the reflecting unit25XA, and ½ wavelength plates 38XC, 38XD for adjusting the polarizationdirections of the −1st diffracted lights DX2, EX2 may be provided in theoptical paths of the diffracted lights DX2, EX2 travelling from thediffraction grating 12 toward the reflecting unit 25XB. The rotationangles of the ½ wavelength plates 38XA, 38XB, 38XC, and 38XD can beadjusted. As an example, the rotation angles of the ½ wavelength plates38XA, 38XC are adjusted so that the light amounts of the diffractedlights DX1, DX2 coming into the diffraction grating 12 after passingthrough the reflecting units 25XA, 25XB and the PBS member 24X aremaximized respectively, and the rotation angles of the ½ wavelengthplates 38XB, 38XD are adjusted so that the light amounts of thediffracted lights EX1, EX2 reflected by the PBS surface A11 of the PBSmember 24X via the reflecting units 25XA, 25XB respectively, aremaximized.

Accordingly, even when the polarization directions of the diffractedlights DX1, EX1, etc., are changed due to the diffraction by thediffraction grating 12, the polarization directions of the diffractedlights DX1, EX1, etc., coming into the PBS member 24X can be optimizedto minimize light amount loss. The diffracted lights DX1, DX2 aretransmitted through the PBS member 24X to come into the diffractiongrating 12, and thus the light amount loss is small even when thepolarization directions of the diffracted lights DX1, DX2 are changed.Therefore, the ½ wavelength plates 38XA, 38XC on the optical paths ofthe diffracted lights DX1, DX2 may be omitted.

Further, as depicted in the main components of a detection head 14A of afirst modification in FIG. 7, instead of using the wedge-shaped prisms34X, 34Y in FIG. 1, a pair of deviation prisms (declination prisms) 46XAand a pair of deviation prisms 46XB may be provided on the optical pathsof the X-axis diffracted lights EX1, EX2 (measuring lights)respectively; a pair of deviation prisms 46YA and a pair of deviationprisms 46YB may be provided on the optical paths of the Y-axisdiffracted lights EY1, EY2 (measuring lights) respectively; and a pairof deviation prisms 46C may be provided on the optical path of themeasuring light for comparison. In the above embodiment, the measuringlight MX and the reference light RX supplied to the detection head 14Aintersect at the angle β and the measuring light MY and the referencelight RY supplied to the detection head 14A intersect at the angle β.Therefore, by adjusting the angles and the inclination directions of thediffracted lights EX1, EX2, EY1, EY2 and the measuring light forcomparison by use of each of the deviation prisms 46XA, 46XB, 46YA,46YB, and 46C to make the diffracted lights EX1, EX2, EY1, EY2 and themeasuring light for comparison parallel to reference lightscorresponding thereto, the S/N ratio of detection signal of theinterference fringes can be improved.

The measuring lights MX, MY may be substantially parallel to thereference lights RX, RY, respectively, the lights MX, MY, RX, and RYbeing supplied to the detection heads 14. In this case, the wedge-shapedprisms 34X, 34Y or the deviation prisms 46XA, 46XB, 46YA, 46YB, and 46Care not required to be provided.

Further, as depicted in the main components of a detection head 14B of asecond modification in FIG. 8, the combining optical members 32X, 33Xmay be provided at the side of the light-exit surface of the PBS member24X in the X-axis interferometer unit 15X, and the interference lights,which are generated by combining the diffracted lights EX1, EX2 and thereference lights RX1, RX2 by the PBS surfaces of the combining opticalmembers 33X, 32X respectively, may come into the optical fibers 39XA,39XB via the polarizing plates 41XA, 41XB, respectively. In thismodification, the reference light RX transmitted through the PBS surfaceA11 of the PBS member 24X comes into the combining optical member 32Xvia an unillustrated wedge-shaped prism and is divided into thereference lights RX1, RX2 by the BS surface of the combining opticalmember 32X. The diffracted lights EX1, EX2 reflected by the PBS surfaceA11 of the PBS member 24X come into the combining optical members 33X,32X respectively.

Similarly, the combining optical members 32Y, 33Y may be provided at theside of the light-exit surface of the PBS member 24Y in the Y-axisinterferometer unit 15Y, and the interference lights, which aregenerated by combining the diffracted lights EY1, EY2 and the referencelights RY1, RY2 by the PBS surfaces of the combining optical members33Y, 32Y respectively, may come into the optical fibers 39YA, 39YB viathe polarizing plates 41YA, 41YB, respectively. In this case also, thereference light RY transmitted through the PBS member 24Y comes into thecombining optical member 32Y via an unillustrated wedge-shaped prism andis divided into the reference lights RY1, RY2 by the BS surface of thecombining optical member 32Y. This construction can further downsize thedetection head 14B.

Second Embodiment

A second embodiment of the present teaching will be explained withreference to FIGS. 9 to 11. FIG. 9 is a schematic view depicting theconstruction of an exposure apparatus EX provided with an encoder deviceaccording to the second embodiment of the present teaching. The exposureapparatus EX is a projection exposure apparatus of the scanning exposuretype constructed of a scanning stepper. The exposure apparatus EX isprovided with a projection optical system PL (projection unit PU). Inthe following explanation, it is assumed that the Z axis is the axisextending in the direction parallel to an optical axis AX of theprojection optical system PL, the Y axis is the axis extending in thedirection in which a reticle R and a wafer W are subjected to therelative scanning in a plane (substantially a horizontal plane)orthogonal to the Z axis, and the X axis is the axis extending in adirection orthogonal to the Z axis and the Y axis.

The exposure apparatus EX is provided with an illumination system 110disclosed, for example, in United States Patent Application PublicationNo. 2003/0025890; and a reticle stage RST which holds a reticle R (mask)illuminated with an illumination light (illumination light beam;exposure light) IL for the exposure (for example, an ArF excimer laserlight beam having a wavelength of 193 nm and a high harmonic wave of asolid-state laser (a semiconductor laser, etc.)) from the illuminationsystem 110. Further, the exposure apparatus EX is provided with theprojection unit PU including the projection optical system PL whichprojects the illumination light IL exiting from the reticle R onto thewafer W (substrate); a stage device 195 including a wafer stage WSTwhich holds the wafer W; a control system; etc. (see FIG. 11).

The reticle R is held to the upper surface of the reticle stage RST bymeans of the vacuum attraction, etc. A circuit pattern, etc., is formedon a pattern surface (lower surface) of the reticle R. The reticle stageRST is finely movable in the XY plane and is capable of being driven inthe scanning direction (Y direction) at a designated scanning velocityby a reticle stage driving system 111, depicted in FIG. 11, includingfor example a linear motor, etc.

The position information (including the positions in the X and Ydirections and the rotational angle in the θz direction) of the reticlestage RST in the movement plane thereof is always detected at aresolution of, for example, about 0.5 nm to about 0.1 nm via a movementmirror 115 (or a mirror-finished side surface of the stage) by a reticleinterferometer 116 including a laser interferometer. A measured value bythe reticle interferometer 116 is sent to a main controller 120,depicted in FIG. 11, constructed of a computer. The main controller 120controls the reticle stage driving system 111 based on the measuredvalue of the reticle interferometer 116 to thereby control the positionand velocity of the reticle stage RST.

In FIG. 9, the projection unit PU arranged at a position below or underthe reticle stage RST is provided with a barrel 140 and the projectionoptical system PL including a plurality of optical elements which areheld in a predetermined positional relation inside the barrel 140. Theprojection optical system PL is, for example, telecentric on the bothsides and has a predetermined projection magnification β (for example,reduction magnification such as ¼, ⅕, etc.). When an illumination areaIAR of the reticle R is illuminated with the illumination light IL fromthe illumination system 110, an image of the circuit pattern in theillumination area IAR of the reticle R is formed via the projectionoptical system PL in an exposure area IA (area conjugated with theillumination area IAR) in one shot area of the wafer (semiconductorwafer) W by the illumination light IL allowed to pass through thereticle R.

Further, the exposure apparatus EX is provided with a nozzle unit 132which constructs a part or portion of a local liquid immersion device108 so as to surround an lower end portion of the barrel 140 holding anend-portion lens 192 which is included in the plurality of opticalelements constructing the projection optical system PL and which is anoptical element closest to the image plane side (closest to the wafer Wside), for the purpose of performing the exposure to which the liquidimmersion method is applied. The nozzle unit 132 is connected to aliquid supply device 186 and a liquid recovery device 189 (see FIG. 11)via a supply tube 131A for supplying a liquid Lq for exposure (forexample, pure water or purified water) and a recovery tube 131B,respectively. Note that when the exposure apparatus EX is an exposureapparatus which is not of the liquid immersion type, the local liquidimmersion device 108 may be omitted.

The wafer stage WST is supported in a non-contact manner via, forexample, a plurality of un-illustrated vacuum pre-loadable pneumaticstatic pressure bearings (air pads) on an upper surface 112 a, of a baseplate 112, which is parallel to the XY plane. The wafer stage WST can bedriven in the X and Y directions by, for example, a stage driving system124 (see FIG. 11) including a planer motor or two pairs of linear motorsorthogonal to each other. Further, the exposure apparatus EX is providedwith a spatial image-measuring system (not depicted) which performsalignment of the reticle R; an alignment system AL (see FIG. 11) whichperforms alignment of the wafer W; a multipoint autofocus sensor 90 (seeFIG. 11) of the oblique incidence system which includes a light-emittingsystem 90 a and a light-receiving system 90 b and which measures thepositions in the Z direction of a plurality of points on a surface ofthe wafer W; and an encoder device 8B which measures positionalinformation of the wafer stage WST.

The wafer stage WST is provided with a body 191 of the wafer stage(stage body 191) which is driven in the X and Y directions; a wafertable WTB arranged on the stage body 191; and a Z-leveling mechanismwhich is provided inside the stage body 191 and which finely drives theposition in the Z direction, the tilt angles in the θx and θy directionsof the wafer table WTB (wafer W) with respect to the stage body 191. Awafer holder (not depicted in the drawing), which holds the wafer W bythe vacuum attraction, etc., on a suction surface substantially parallelto the XY plane, is provided on the wafer table WTB at an upper andcentral portion of the wafer table WTB.

Further, a flat plate-shaped plate body 128 having a high flatness isprovided on the upper surface of the wafer table WTB. The plate body 128has a surface (or a protective member) which is subjected to theliquid-repellent treatment for the liquid Lq and which is provided to besubstantially flush with the surface of the wafer (wafer surface) placedon the wafer holder. The outer shape (contour) of the plate body 128 isrectangular, and a circular-shaped opening is formed in the centralportion of the plate body 128, the opening being greater to some extentthan the wafer holder (a wafer-placement area).

Note that in the structure of the exposure apparatus of the so-calledliquid immersion type which is provided with the local liquid immersiondevice 108 as described above, the plate body 128 further has a plateportion (liquid-repellent plate) 128 a which has a rectangular outershape (contour) surrounding the circular-shaped opening, and which has asurface subjected to the liquid-repellent treatment; and a peripheryportion 128 e surrounding the plate portion 128 a, as depicted in FIG.10 that is a plan view of the wafer table WTB (wafer stage WST). A pairof two-dimensional diffraction gratings 12A, 12B and a pair oftwo-dimensional diffraction gratings 12C, 12D are arranged on the uppersurface of the periphery portion 128 e. The pair of diffraction gratings12A, 12B are elongated in the X direction so as to sandwich the plateportion 128 a therebetween in the Y direction; and the pair ofdiffraction gratings 12C, 12D are elongated in the Y direction so as tosandwich the plate portion 128 a therebetween in the X direction. Eachof the diffraction gratings 12A to 12D is a reflective-type diffractiongrating having a two-dimensional grating pattern of which periodicdirections are the X and Y directions, similar to the diffractiongrating 12 depicted in FIG. 1.

Further, in FIG. 9, a measurement frame 150 which is flat plate-shapedand which is substantially parallel to the XY plane is supported, via aconnection member (not depicted in the drawing) by a frame (not depictedin the drawing) supporting the projection unit PU. A plurality ofdetection heads 14 having the same construction as that of thethree-axis detection head 14 depicted in FIG. 1 is fixed to the bottomsurface of the measurement frame 150 so that the plurality of detectionheads 14 sandwich the projection optical system PL in the X direction;and a plurality of detection heads 14 having the same construction asthat of the three-axis detection head 14 depicted in FIG. 1 is fixed tothe bottom surface of the measurement frame 150 so that the plurality ofdetection heads 14 sandwich the projection optical system PL in the Ydirection (see FIG. 10). Further, there are also provided one lasersource or a plurality of laser sources (not depicted) similar to thelaser light source 16 in FIG. 1 for supplying a laser light or laserlight beam (measuring light and reference light) to the plurality ofdetection heads 14.

In FIG. 10, the Exposure apparatus EX is constructed such that, during aperiod in which the wafer W is being exposed with the illumination lightfrom the projection optical system PL, any two of the plurality ofdetection heads 14 in a row A1 in the Y direction always face or areopposite to the diffraction gratings 12A and 12B and any two of thedetection heads 14 in a row A2 in the X direction always face or areopposite to the diffraction gratings 12C and 12D. Each of the detectionheads 14 in the row A1 irradiates the measuring light to the diffractiongrating 12A or 12B, and supplies the detection signal of theinterference light, generated by interference between the diffractedlight generated from the diffraction grating 12A or 12B and thereference light, to one of measurement calculation units 42 (see FIG.11) corresponding thereto. In a similar manner with the measurementcalculation unit 42 depicted in FIG. 1, these measurement calculationunits 42 obtain the relative positions (relative movement amounts) inthe X, Y and Z directions of the wafer stage WST relative to themeasurement frame 150 at a resolution of, for example, 0.5 nm to 0.1 nm,and supply the respective measured values to a measured value-switchingunit 80A. The measured value-switching unit 80A supplies, to the maincontroller 120, the information about the relative positions suppliedfrom measurement calculation units 42, among the measurement calculationunits 42, corresponding to the detection heads 14 facing the diffractiongratings 12A and 12B, respectively.

Further, each of the detection heads 14 corresponding to or aligned inthe row A2 irradiates the measuring light to the diffraction gratings12C or 12D, and supplies the detection signal of the interference light,generated by interference between the diffracted light generated fromthe diffraction grating 12C or 12D and the reference light, to one ofmeasurement calculation units 42 (see FIG. 11) corresponding thereto. Ina similar manner with the measurement calculation unit 42 depicted inFIG. 1, these measurement calculation units 42 obtain the relativepositions (relative movement amounts) in the X, Y and Z directions ofthe wafer stage WST relative to the measurement frame 150 at aresolution of, for example, 0.5 nm to 0.1 nm, and supply the respectivemeasured values to a measured value-switching unit 80B. The measuredvalue-switching unit 80B supplies, to the main controller 120, theinformation about the relative positions supplied from measurementcalculation units 42, among the measurement calculation units 42,corresponding to the detection heads 14 facing the diffraction gratings12C and 12D, respectively.

A three-axis encoder 10A is constructed of the plurality of detectionheads 14 in the row A1, the laser light source (not depicted), themeasurement calculation units 42 and the diffraction gratings 12A and12B; and a three-axis encoder 10B is constructed of the plurality ofdetection heads 14 in the row A2, the laser light source (not depicted),the measurement calculation units 42 and the diffraction gratings 12Cand 12D. Further, the encoder device 8B is constructed of the three-axisencoders 10A and 10B and the measured value-switching units 80A and 80B.The main controller 120 obtains information about the position in the X,Y and Z directions, the rotational angle in the Oz direction, etc. ofthe wafer stage WST with respect to the measurement frame 150 (theprojection optical system PL), based on the information about therelative positions supplied from the encoder device 8B; and the maincontroller 120 drives the wafer stage WST via the stage driving system124 based on these information.

When performing exposure by the exposure apparatus EX, at first, thereticle R and the wafer W are aligned with respect to each other. Afterthat, an image of the pattern of the reticle R is transferred onto oneshot area on the surface of the wafer W by performing a scanningexposure operation wherein the irradiation of the illumination light ILonto the reticle R is started and an image of a portion or part of thepattern of the reticle R is projected onto the one shot area via theprojection optical system PL, while the reticle stage RST and the waferstage WST are synchronously moved in the Y direction (subjected tosynchronous scanning) at a velocity ratio of the projectionmagnification β of the projection optical system PL. After that, theoperation in which the wafer W is step-moved in the X direction and theY direction via the wafer stage WST and the scanning exposure operationdescribed above are repeated. By doing so, the pattern image of thereticle R is transferred onto all the shot areas of the wafer W in thestep-and-scan manner and based on or using the liquid immersion method.

At this time, the optical path lengths of the measuring light and thediffracted light in each of the detection heads 14 in the encoder device8B are shorter than those in the laser interferometer. Therefore, theinfluence caused due to the fluctuation of the air and affecting themeasured values obtained by using the detection heads 14 is very small.Thus, since the encoder device 8B of the embodiment has in particularexcellent measurement stability in such a short term that the air isfluctuated (excellent short-term stability) as compared to the laserinterferometer, it is possible to transfer the image of the pattern ofthe reticle R onto the wafer W highly precisely. Further, each of thedetection heads 14 is capable of detecting the signal including theinformation about the relative moving amount always with high S/N ratio,even when the position in the Z direction of one of the diffractedgratings 12A to 12D is changed. Therefore, the wafer stage WST can bedriven always with a high precision.

Note that in this embodiment, the detection heads 14 are arranged on theside of the measurement frame 150, and the diffraction gratings 12A to12D are arranged on the side of the wafer stage WST. As anotherconfiguration different from the above-described configuration, it isallowable to arrange the diffraction gratings 12A to 12D on the side ofthe measurement frame 150 and to arrange the detection heads 14 on theside of the wafer stage WST. Alternatively, the diffraction gratings 12Ato 12D may be arranged on the back surface of the wafer stage WST andthe detection heads 14 may be arranged on the side closer to a surfacetable than the wafer stage WST.

Further, when the position information of the reticle stage RST isobtained, the encoder described in this embodiment may be used insteadof or in conjunction with the reticle interferometer 116.

Further, in a case that an electronic device (or a micro device) such asa semiconductor device is produced by using the exposure apparatus EX orthe exposure method as referred to in the embodiments described above,the electronic device is produced, as shown in FIG. 13, by performing: astep 221 of designing the function and the performance of the electronicdevice; a step 222 of manufacturing a reticle (mask) based on thedesigning step; a step 223 of producing a substrate (wafer) as a basematerial for the device and of coating the substrate with a resist; asubstrate-processing step 224 including a step of exposing the substrate(photosensitive substrate) with the pattern of the reticle by theexposure apparatus (exposure method) in the above embodiment(s), a stepof developing the exposed substrate, a step of heating (curing) andetching the developed substrate, and the like; a step 225 of assemblingthe device (including processing processes such as a dicing step, abonding step, a packaging step, etc.); an inspection step 226; and thelike.

In other words, the method for producing the device includes thelithography step of transferring the image of the pattern of the reticleonto the substrate (wafer) by using the exposure apparatus EX (exposuremethod) of the above embodiments and developing the exposed substrate;and the step of processing the substrate, onto which the image of thepattern has been transferred, based on the image of the pattern (theetching, etc. in the step 224). According to the embodiments, since theposition of the wafer stage WST of the exposure apparatus EX can becontrolled with a high precision, it is possible to produce theelectronic device highly precisely.

Further, the encoder 10 of each of the embodiments is applicable to anoptical apparatus, other than the exposure apparatus, including: anoptical system (optical system collecting a laser light, etc.) for anobject-to-be-inspected or processed (inspection objective or processingobjective), and a moving device (stage, etc.) which moves theobject-to-be-inspected or processed, such as an inspection apparatus, ameasuring apparatus, or the like, so that the encoder 10 measures arelative moving amount of the moving device (object-to-be-inspected orprocessed) relative to, for example, the optical system.

In the above embodiments, the explanation has been made by citing thestep-and-scan projection exposure apparatus as an example, but thepresent teaching is applicable to the encoder in the step-and-repeatprojection exposure apparatus.

The illumination light IL is not limited to the ArF excimer laser lightbeam (wavelength: 193 nm), and it is allowable to use ultraviolet lightsuch as the KrF excimer laser light beam (wavelength: 248 nm) or vacuumultraviolet light such as the F₂ laser light beam (wavelength: 157 nm).For example, as disclosed in the specification of U.S. Pat. No.7,023,610, it is also appropriate to use the harmonic wave as the vacuumultraviolet light, the harmonic wave being obtained by amplifying thesingle wavelength laser beam which is in the infrared region or thevisible region and which is oscillated from the fiber laser or the DFBsemiconductor laser with, for example, a fiber amplifier doped witherbium (or both of erbium and ytterbium) and performing the wavelengthconversion to convert the amplified laser beam into the ultravioletlight by using the nonlinear optical crystal.

Further, the above embodiments can be applied also to an exposureapparatus using charged particle radiation such as the electron beam orthe ion beam.

In the embodiments described above, the light-transmissive type mask(reticle) is used, in which a predetermined light-shielding pattern (orphase pattern or dimming or light-reducing pattern) is formed on thelight-transmissive substrate. However, instead of this reticle, asdisclosed, for example, in the specification of U.S. Pat. No. 6,778,257,it is also allowable to use an electronic mask (also referred to as“variable shaped mask”, “active mask”, or “image generator”, andincluding, for example, Digital Micro-mirror Device (DMD) as a kind ofthe non-light emission type image display device (spatial lightmodulator)) on which a transmissive pattern, a reflective pattern, or alight-emitting pattern is formed based on the electronic data of thepattern to be subjected to the exposure. In a case that such a variableshaped mask is used, a stage on which a workpiece such as the wafer orthe glass plate is placed is scanned relative to the variable shapedmask. Thus, it is possible to obtain the effect equivalent to the aboveembodiments by measuring the position of the stage by use of the encodersystem.

For example, each of the embodiments of the present teaching isapplicable to an exposure apparatus (lithography system), such asdisclosed in International Publication No. 2001/035168, in which aline-and-space pattern is formed on a wafer W by forming interferencefringes on the wafer W.

Further, for example, each of the embodiments of the present teaching isapplicable to an exposure apparatus, such as disclosed in thespecification of U.S. Pat. No. 6,611,316, in which two reticle patternsare combined (synthesized) on a wafer via a projection optical system,and one shot area on the wafer is subjected to the double exposuresubstantially simultaneously by means of one time of the scanningexposure.

In the embodiments described above, the object on which the pattern isto be formed (object as the exposure objective to be irradiated with theenergy beam) is not limited to the wafer. The object may be any otherobject including, for example, glass plates, ceramic substrates, filmmembers, and mask blanks.

The present teaching is not limited to the application to the exposureapparatus for producing the semiconductor device. The present teachingis also widely applicable, for example, to the exposure apparatus fortransferring a liquid crystal display elements pattern onto arectangular glass plate and the exposure apparatus for producing theorganic EL, the thin film magnetic head, the image pickup device (forexample, CCD), the micromachine, the DNA chip, and the like. Further,each of the above embodiments of the present teaching is applicable notonly to the micro device such as the semiconductor device, but also tothe exposure apparatus which transfers the circuit pattern, for example,to the glass substrate or the silicon wafer in order to produce thereticle or the mask to be used, for example, for the optical exposureapparatus, the EUV exposure apparatus, the X-ray exposure apparatus, andthe electron beam exposure apparatus.

The measuring apparatus and the exposure apparatus of each of theembodiments is produced by assembling the various subsystems includingthe respective constitutive elements as recited in claims of thisapplication so that the predetermined mechanical accuracy, theelectrical accuracy, and the optical accuracy are maintained. In orderto secure the various accuracies, those performed before and after theassembling include the adjustment for achieving the optical accuracy forthe various optical systems, the adjustment for achieving the mechanicalaccuracy for the various mechanical systems, and the adjustment forachieving the electrical accuracy for the various electrical systems.The steps of assembling the various subsystems into the exposureapparatus include, for example, the mechanical connection, the wiringconnection of the electric circuits, and the piping connection of theair pressure circuits among the various subsystems. It goes withoutsaying that the steps of assembling the respective individual subsystemsare performed before performing the steps of assembling the varioussubsystems into the exposure apparatus. When the steps of assembling thevarious subsystems into the exposure apparatus are completed, theoverall adjustment is performed to secure the various accuracies of theentire exposure apparatus. It is also appropriate that the exposureapparatus is produced in a clean room in which, for example, thetemperature and the cleanness are managed.

The disclosures of all of the above-mentioned patent documents,International Publications, United States Patent Publications, andUnited States Patents, those of which concern the exposure apparatus andthe like are incorporated herein by reference in their entireties.

The entire disclosure contents of U.S. Patent Application No. 61/638,719filed on Apr. 26, 2012 including the specification, claims, drawings,and abstract are incorporated by reference in this application in theirentireties.

Note that it is a matter of course that the present teaching is notlimited to the embodiments described above, and may be embodied in othervarious forms within a scope without deviating from the gist oressential characteristics of the present teaching.

According to the embodiments described above, since the first diffractedlight is allowed to come into the diffraction grating via the firstreflecting unit and the third diffracted light is allowed to come intothe diffraction grating via the second reflecting unit, even when theheight of the grating pattern surface of the diffraction gratingrelative to the first reflecting member is changed or varied, it ispossible to reduce a relative shift amount between the second diffractedlight generated, via diffraction of the first diffracted light, from thediffraction grating and other light beam than the second diffractedlight and a relative shift amount between the fourth diffracted lightgenerated, via diffraction of the third diffracted light, from thediffraction grating and other light beam than the fourth diffractedlight. Therefore, it is possible to prevent the lowering of signalintensity of the interference light with respect to the change in theheight of the grating pattern surface of the diffraction grating,thereby making it possible to maintain high measurement precision oraccuracy.

What is claimed:
 1. An optical system for an encoder device configuredto measure a relative moving amount relative to a reflective-typediffraction grating, the optical system comprising: a first opticalmember configured to split a light from a light source into a first partand a second part different from the first part, emit the first part asa measuring light so as to irradiate the diffraction grating with themeasuring light, and emit the second part as a reference light, thelight from the light source coming into the first optical member via aninput optical system, the reference light being generated based on thesecond part without diffracting the second part at the diffractiongrating; and a second optical member configured to cause a diffractedlight, which is generated via a diffraction of the measuring light atthe diffraction grating, to come into the first optical member, whereinthe first optical member emits the diffracted light from the secondoptical member in a direction in which the reference light is emitted sothat the diffracted light comes into an output optical system; and thefirst optical member is positioned between the input optical system andthe output optical system.
 2. The optical system according to claim 1,wherein the first optical member is configured to reflect one of thereference light and the diffracted light from the second optical memberand transmit other of the reference light and the diffracted light fromthe second optical member through the first optical member.
 3. Theoptical system according to claim 2, wherein the first optical memberincludes a polarized beam splitter.
 4. The optical system according toclaim 1, wherein the second optical member is configured to cause afirst diffracted light, which is generated based on the measuring lightwhich irradiates the diffraction grating, to come into the diffractiongrating, and cause a second diffracted light, which is generated basedon the first diffracted light coming into the diffraction grating, tocome into the first optical member.
 5. The optical system according toclaim 4, wherein the second optical member includes a plurality ofreflection surfaces.
 6. The optical system according to claim 1, furthercomprising a third optical member which is arranged such that the firstoptical member is interposed between the second and third opticalmembers, and which is configured to cause a diffracted light generatedfrom the diffraction grating to come into the first optical member. 7.The optical system according to claim 4, further comprising a thirdoptical member which is arranged such that the first optical member isinterposed between the second and third optical members, and which isconfigured to cause a third diffracted light, which is generated basedon the measuring light which irradiates the diffraction grating, to comeinto the diffraction grating and cause a fourth diffracted lightgenerated based on the third diffracted light coming into thediffraction grating to come into the first optical member.
 8. Theoptical system according to claim 1, wherein the first optical memberincludes a polarization splitting surface, and one of the measuringlight and the reference light travels through the polarization splittingsurface and other of the measuring light and the reference light arereflected by the polarization splitting surface.
 9. An encoder devicewhich measures a relative moving amount between a first member and asecond member, the encoder device comprising: a light source configuredto generate a measuring light and a reference light; a reflection-typediffraction grating which is provided on the first member and whichincludes a grating pattern having a periodic direction in at least afirst direction; an optical system as defined in claim 1; and a lightreceiving unit configured to receive a light emitted from the opticalsystem.
 10. An exposure apparatus which exposes a pattern onto an objectto be exposed, the exposure apparatus comprising: a frame; a stage whichis configured to support the object to be exposed and which is movablerelative to the frame at least in a first direction; and an encoderdevice as defined in claim 9 configured to measure a relative movingamount between the frame and the stage at least in the first direction.11. A device manufacturing method comprising a lithography step in whichan object is exposed by using an exposure apparatus as defined in claim10.
 12. The optical system according to claim 1, further comprising theinput optical system and the output optical system.